I have found an issue upgrading from Windows 7 to Windows 10.
When from Android device I connect to a Windows 7 PC the issue does not occours,
instead, when I connect to a Windows 10 laptop, in touch mode, it is not possible to zoom using the PINCH gesture.
What kind of teamviewer do you run? Becouse from teamviewer 10 and down there are problems with the cumulative update from windows 10 so maybe that is the problem.
Have you tried uninstalling your teamviewer on both your phone and the pc (you need to select delete my settings as wel)? If not you could do that with this trick,
I hope this helps!